Muscadine grapes, native to the southeastern U.S., are prized for their thick skin, nutritional value, and natural resistance to pests. However, their uneven ripening and individual fruit drop make them difficult to harvest mechanically, keeping them largely confined to regional markets. Unlike bunch grapes, muscadines must be picked one by one before they fall naturally—an expensive, labor-intensive process. Earlier efforts to adapt mechanical harvesting to muscadines were hampered by limited knowledge of their fruit detachment biology. Prior studies measured detachment force but did not examine underlying tissue structures or genetic factors. Due to these limitations, there is a critical need to uncover the biological basis of muscadine abscission to enable cost-effective, automated harvest solutions.
In a collaborative effort, scientists from the University of Florida and the University of Georgia have mapped the anatomical and genetic landscape of muscadine grape detachment. Their study (DOI: 10.1093/hr/uhae227), published in Horticulture Research on August 9, 2024, reveals how structural traits and gene networks influence fruit abscission. By comparing grapes that hold tight to their stems with those that let go more easily, the team identified key morphological indicators and candidate genes. The research marks a major step toward making muscadine grapes more amenable to mechanical harvesting—potentially transforming the economics of this specialty crop.
The team analyzed 18 muscadine genotypes, measuring fruit detachment force (FDF) at four developmental stages. They found three distinct patterns of FDF change, with most varieties showing the steepest decline between veraison and full maturity. Physical measurements showed that fruit with longer pedicels, larger diameters, and wider junction areas had significantly higher FDF, indicating they were harder to detach. To investigate the molecular underpinnings, the researchers performed transcriptome analysis on two contrasting genotypes: one with strong attachment and one with weak. The weakly attached genotype showed increased expression of genes involved in jasmonic acid biosynthesis, including VvJMT, which is known to promote abscission. Transcription factor analysis highlighted bHLH, MYB, and ERF families as major players in abscission-related gene regulation. Further validation came from Arabidopsis mutants. Loss of the CAD9 gene, homologous to VvCAD6 in muscadine, resulted in delayed floral organ abscission, linking lignin biosynthesis to detachment processes. Scanning electron microscopy confirmed that weakly attached fruit exhibited greater tissue breakdown and reduced vascular bundle integrity in the abscission zone. Together, the physical, anatomical, and molecular data converge to reveal the complex biology of muscadine detachment and identify promising targets for breeding and biotechnology.
“This research gives us an unprecedented view into what controls fruit detachment in muscadines—from stem thickness to gene expression,” said Dr. Ali Sarkhosh, senior author and horticultural scientist at the University of Florida. “With these insights, breeders can focus on specific traits and genes to develop muscadine varieties that are better suited for machine harvest. That’s a game-changer for growers who want to reduce costs without sacrificing fruit quality.”
By identifying the traits and genes that influence how easily muscadine grapes let go, this study opens new possibilities for breeding cultivars tailored to mechanical harvesting. Growers could reduce their reliance on manual labor while preserving fruit integrity—a crucial factor for the fresh market. The research also lays a foundation for genetic tools or chemical cues that could time or enhance abscission, making harvest even more efficient. As labor costs continue to rise, these findings offer a practical path toward sustainable and scalable muscadine production in the southeastern U.S. and beyond.
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References
DOI
10.1093/hr/uhae227
Original Source URL
https://doi.org/10.1093/hr/uhae227
Funding information
This work was supported by USDA-NIFA GRANT # 2021-67021-34484 to A.B. and T.L.
About Horticulture Research
Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.